Fluid bed combustor for operation at ash fusing temperatures

ABSTRACT

A fluidized bed combustor is disclosed which includes means for preventing the agglomeration of sticky ashes, salts and molten metals entrained in exhaust gases on the interior surfaces of the combustion chamber and exhaust system used for venting the exhaust products from the combustion chamber. A fluidized bed is disposed within the combustion chamber which has intake and exhaust sides. A pressurized air supply is coupled to the intake side of the fluidized bed to force oxygen into the fluidized bed. A pressurized source of shredded solid waste material is also coupled to the intake side of the fluidized bed to promote waste burning. An exhaust system having an outwardly flared opening located remote from the dome and the side wall of the combustion chamber couples the exhaust gases and entrained sticky ashes, salts and molten metals to a second chamber which contains a low velocity centrifugal separator. The bottom of the second chamber contains an apparatus for collecting the sticky ashes, salts and molten metals. A valve mechanism also located in the bottom of the second chamber periodically empties the collected materials therefrom. A cooling water jacket is provided around the collecting apparatus to quench the collected materials.

United States Patent Gold bach FLUID BED COMBUSTOR FOR OPERATION AT ASHFUSING TEMPERATURES [75] Inventor: Gerhardt O. Goldbach, San Jose.

Calif.

[73] Assignee: Government of the United States Environmental ProtectionAgency, Washington, DC.

[22] Filed: Oct. 30, 1974 [2!] Appl. No.: 519,328

[52] US. Cl 110/8 F; l/28 J [51] Int. Cl. F236 5/00 [58] Field of Search[IO/8 R, 8 F, 28 J; [22/4 D; 34/57 R. 57 A [56] References Cited UNlTEDSTATES PATENTS 2,958,298 ll/l96O Mayers 110/28 3,366,080 H1968 Albertson110/8 3.589.313 6/l97l Smith et al 4 A l l lO/S 3.779,]81 12/[973Staffin ct al. s llO/S 3.818.846 6/[974 Reese llO/8 PrimaryExaminer-Kenneth W. Sprague [57] ABSTRACT A fluidized bed combustor isdisclosed which includes means for preventing the agglomeration ofsticky ashes, salts and molten metals entrained in exhaust gases on theinterior surfaces of the combustion chamber and exhaust system used forventing the exhaust products from the combustion chamber A fluidized bedis disposed within the combustion chamber which has intake and exhaustsides. A pressurized air supply is coupled to the intake side of thefluidized bed to force oxygen into the fluidized bed. A pressurizedsource of shredded solid waste material is also coupled to the intakeside of the fluidized bed to promote waste burning. An exhaust systemhaving an outwardly flared opening located remote from the dome and theside wall of the combustion chamber couples the exhaust gases andentrained sticky ashes, salts and molten metals to a second chamberwhich contains a low velocity centrifugal separator. The bottom of thesecond chamber contains an apparatus for collecting the sticky ashes,salts and molten metals. A valve mechanism also located in the bottom ofthe second chamber periodically empties the collected materialstherefrom. A cooling water jacket is provided around the collectingapparatus to quench the collected materials.

6 Claims, 2 Drawing Figures WATER FLUID BED COMBUSTOR FOR OPERATION ATASH FUSING TEMPERATURES BACKGROUND OF THE INVENTION l. Field of theInvention The invention relates to fluid bed combustors which burn solidwastes. More particularly, the invention relates to fluid bed combustorsof the type which burn shredded solid wastes that produce sticky ashes,salts and molten metals having a temperature at or above the ash fusingtemperature and which contain apparatus for preventing the agglomerationof these materials on the surfaces of the combustion chamber and theexhaust system of the combustor.

2. Description of the Prior Art Apparatus for burning solid wastes havebeen well known for many years. The high combustion tempera tures of theprior art apparatus produced sticky ashes, salts and molten metalshaving a temperature at or above the ash fusing temperature. When wasteburning systems were continually operated at or above the ash fusingtemperature, the resultant sticky ashes, salts and molten metalscontained within the exhaust gases formed slag within the combustionchamber and large clinkers which blocked the pipes of the exhaust systemor which fell back into the combustion chamber. Removal of thesematerials involved a large amount of down time and prevented theefficient useage of the combustion apparatus to its full capacity.

Attempts have been made in the prior art apparatus to prevent theformation of sticky solid wastes on the blades of turbines by loweringthe intake gas tempera ture below the ash fusion temperature. Anexemplary apparatus is disclosed in US. Pat. No. 3,309,866, issued toKydd. That apparatus uses flameless combustion to prevent thetemperature of the intake gas from rising to the ash fusing temperature.

Other attempts to solve the problem of accretion of sticky solids onturbine blades have involved the use of filters. The surface of thefilter is disposed within the intake gas stream of the turbine to effectseparation of sticky ashes. The filter is then plunged into water torapidly cool the surfaces which have solids formed thereon to the pointwhere the accretion flakes off and settles into the water. The cleanedfilter is then removed from the water and is again disposed within theexhaust gas stream. US. Pat. No. 3,550,372, issued to Craig is exemplaryof this type of system.

US. Pat. No. 2,616,256, issued to Davy, et al. discloses apparatus forremoving solids from the intake gases of turbines by using centrifugalforce. Solid fuel is introduced into a primary combustion chamber and istherein burned at temperatures above the ash fusing temperature. Theshape of the primary combustion chamber imparts a high circumferentialvelocity to the combustion products contained therein. The resultantcentrifugal force exerted upon the sticky ashes contained within theprimary combustion chamber causes their impingement and accretion uponthe side walls of the primary combustion chamber. The resultant ash filmflows downwardly by gravity where it is trapped by a truncated conicalwall. Gases containing the remaining sticky ash particles flow through acentrally disposed exhaust port which is located in the bottom of theprimary combustion chamber into a second combustion chamber. Thereinthey are cooled by air tempering and moved toward the bottom of thechamber where solidified ash particles are collected. Periodically thesolid ash particles are removed from the second combustion chamber bythe opining of a valve mechanism.

Each of the prior art solutions for preventing the accretion of stickyashes on the interior surfaces of com bustion chambers differssubstantially from the present invention. Unlike the present invention,none of the prior art exemplified by the aforementioned patents preventsthe accretion of solids on interior combustion and exhaust surfaces bylimiting the velocity of the exhaust gases and entrained solids below avelocity which causes them to stick to the interior surfaces of thecombustion chamber and the exhaust system from impact.

SUMMARY OF THE INVENTION The disadvantages and limitations of the priorart are obviated by the present invention which provides an apparatusfor burning shredded solid wastes that prevents the accretion of stickyashes, salts and molten metals on the interior surfaces of thecombustion chamber and the associated exhaust system. Accretion ofsolids on the interior surfaces of the combustion chamber and theexhaust system is prevented by main taining the velocity of the exhaustgases and entrained solids below a velocity which imparts sufficientinertia to them to cause their adhesion because of impact on thesesurfaces.

In this specification, the terminology ash fusion temperature" definesthe temperature at which solids resulting from combustion becomeadherent to sur faces.

An apparatus constructed according to the present invention includes acombustion chamber which contains a fluidized bed having intake andexhaust sides. A source of pressurized air and a source of pressurizedshredded solid waste is coupled to the intake side of the fluidized bed.The exhaust side of the fluidized bed opens up into the freeboardsection of the combustion chamber. The freeboard section is enclosed bythe exhaust side of the fluidized bed, the side walls, and the dome ofthe combustion chamber. An exhaust system is mounted in the side wall ofthe combustion chamber. The exhaust system includes an exhaust pipedisposed within the combustion chamber which has an opening that isoutwardly flared and located remote from the dome and the side wall toprevent the direct impingement of entrained solids contained within theexhaust gas thereon. The outwardly flared shape of the opening preventsthe entrained solids contained within the ex haust gases which traversethe freeboard section of the combustion chamber from impringing at anangle of incidence on the interior surface of the opening which is nearthe perpendicular. As a result, the solids tangentially strike theinterior surface of the opening.

A second chamber is provided which has part of the exhaust systemdisposed therein. The part of the exhaust system contained within thechamber forms a low velocity centrifugal separator which has a dischargeport disposed within the second chamber. The low velocity centrifugalseparator is formed from a semicircular section of pipe having arelatively large radius. In terms of the specification, the terminology"low velocity centrifugal separator" defines a centrifugal separator inwhich the velocity of gases and entrained solids passing therethrough isbelow a velocity which causes their adherence to its interior surfacesbecause of centrifugal force. The discharge port of the exhaust systemopens toward the bottom of the chamber. Disposed within the bottom ofthe chamber is a removal conduit having an intake port located withinthe chamber and an exhaust port coupled to a ball valve mechanism.Coupled to the ball valve mechanism is an intermediate air lock havingan intake port which is coupled to the removal conduit and an exhaustport which is coupled to a second ball valve mechanism. The first andsecond ball valve mechanisms are periodically opened to re move solidswhich have collected in the bottom of the chamber that have been cooledbelow the ash fusing temperature. Cooling of collected solids isaccomplished by a water jacket which is mechanically cou' pled to theremoval conduit and to the intermediate air lock. Exhaust gases areremoved from the chamber by an exhaust system which includes an openingdisposed within the second chamber that is outwardly flared and locatedremote from the top, bottom and side walls. The discharge port of theexhaust network opens to the exterior of the second chamber. Acollecting cone is disposed in the bottom of the second chamber forguiding solids which have been discharged from the discharge port of theexhaust system into the intake opening of the removal conduit. A largemesh conical screen is disposed in the bottom of the chamber to preventlarge clinkers from entering the intake opening of the removal conduit.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a section of the front viewof the present invention; and

FIG. 2 is a partial section of the top view of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGS. I and 2, afluid bed combustor for operation at ash fusing temperatures constructedaccording to the present invention is described as follows. Combustionchamber 12 is provided with a fluidized bed 14 having an intake side 16and an exhaust side 18. A source of pressurized air 20 and a source ofpressurized shredded solid waste 22 is coupled to the intake side I6 offluidized bed 14. Pressurized air coming from source 20 initially passesinto plenum chamber 24 and then passes through a perforated distributorplate 26 disposed in the bottom of the fluidized bed 14. The highpressure source of air 20 upon passing through the distributor plate 26fluidizes the bed of sand contained within fluidized bed 14. Part of thepressurized air supply from source 20 is bled off through pipe 28 toentrain shredded solid waste injected by source 22 into pipe 28. Theshredded solid waste and air pass into the fluidized bed where they arecombusted at temperatures well above the ash fusing temperature.Contained within the solid wastes which are combusted in the fluidizedbed 14 are non-ferrous metals that melt below 1,400F.. substances whichproduce sticky ashes, and salts that are sticky or molten at thecombustion temperature which are maintained within the fluidized bed.The burning materials pass through the exhaust portion 18 of thefluidized bed 14 into the freeboard 30 of the combustion chamber 12. Thefreeboard portion 30 of the combustion chamber 12 is enclosed by wallsection 32, dome 34 and exhaust side 18 of the fluidized bed 14.

The exhaust system 36 of the combustion chamber 12 and chamber 42 of thepresent invention is described with reference to FIGS. 1 and 2. Pipe 38of the exhaust system 36 extends through the side wall 32 of thecombustion chamber 12 to form an outwardly flared opening 40 which islocated remote from the side wall 32 and dome 34 of the combustionchamber 12. The remaining part of exhaust pipe 38 opens into chamber 42.The position of exhaust pipe 38 contained within chamber 42 comprises alow velocity centrifugal separator 44. The low velocity centrifugalseparator 44 is constructed from a relatively large radius of curvature.The end of centrifugal separator 44 opens into chamber 42 throughdischarge port 46. The portion of chamber 42 below discharge port 46 iscomprised of side wall 48 and bottom section 50. A conical collectingcone 52 is located in the bottom of chamber 42. The base of conicallarge mesh screen 54 is joined to the surface of conical collecting cone52. Disposed in the bottom center of chamber 52 at the apex of collecting cone 52 is removal conduit 56. The intake port of removal conduit 56opens into the apical section of the collecting cone 52. The exhaustport of removal conduit 56 opens into ball valve mechanism 58. Ballvalve mechanism 58 opens into the intake port of intermedi ate air lock60. The exhaust port of intermediate air lock 60 opens into ball valvemechanism 62. A source of coolant 64 is coupled to the removal conduit56 and to the intermediate air lock 60. Disposed in the side wall 48 ofchamber 42 is an exhaust system 66 having an outwardly flared opening 68which opens into chamber 42 remote from the side wall 48. The outwardlyflared opening 68 of the second chamber 42 is designed to perform thesame function as outwardly flared opening 40 of the combustion chamber12. The exhaust system 66 has a discharge port opening to the exteriorof chamber 42.

OPERATION The operation of the present invention is as follows: Acombustible mixture of air and shredded solid waste is introduced intofluidized bed I4, where, in the course of normal combustion, stickyashes, sticky salts and molten metals and exhaust gases are produced.The combustion products pass into the freeboard section 30 and throughthe outwardly flared opening 40 of exhaust system 38. The inner contourof opening 40 prevents perpendicular or near perpendicular impingementof the solids onto the interior surface of opening 40. The tangential ornear tangential impingement of solids on the interior surface of opening40 prevents their accretion thereon. The entrained solids and exhaustgases pass through low velocity centrifugal separator 44. The velocityof the entrained sticky ashes within the centrif ugal separator 44 ismaintained below the velocity which produces a centrifugal force thatcauses accretion of the sticky solids on the interior surface of thecentrifugal separator. The entrained solids pass through discharge port46 and collect in removal conduit 56. Conical large mesh screen 54prevents large clinkers from entering the removal conduit 56. Removalconduit 56 is cooled to quench the solids collected therein.Periodically, ball valve 58 opens to allow the ashes contained inremoval conduit 56 to pass into intermediate airlock 60 and then closes,Intermediate airlock is cooled to further quench the collected solids.Ball valve 62 then opens to permit removal of the cooled solids. Theexhaust gases pass from chamber 42 through opening 68 of exhaust system66.

It has been discovered that the elutriation of sand from the fluidizedbed 14 scours the surfaces of the freeboard 30, exhaust system 36 andthe second chamber 42 to help remove residual accretion.

While the preferred embodiment of the invention relates to fluidized bedcombustors for burning shredded waste, it should be apparent to thosepersons skilled in the art to which the invention pertains that theteachings of the invention are applicable to all types of combustionsystems wherein agglomeration of sticky ashes have been a problem.

What is claimed is:

I. In a fluidized bed combustor which burns waste materials of the typethat produce sticky ashes, salts and molten metals which form slag thatadheres to the interior surfaces of the combustor, the combinationcomprising:

a. a fluidized bed disposed within a combustion chamber having intakeand exhaust sides;

b. a pressurized air supply coupled to the intake side of said fluidizedbed;

c. a pressurized source of waste material coupled to the intake side ofsaid fluidized bed;

d. means coupled to said exhaust side of said fluidized bed for removingsaid sticky ashes, salts and molten metals and exhaust gases from saidcombustion chamber while they are at or above the temperature at whichthe sticky ashes, salts and molten metals begin to adhere to saidinterior surfaces of the combustor, said means comprising an exhaustsystem which maintains the velocity of said sticky ashes, salts andmolten metals entrained within said exhaust gas below a velocity whichproduces their agglomeration on interior surfaces of said combustionchamber and said exhaust system.

2. In a combustor as recited in claim 1 wherein:

a. said combustion chamber on the exhaust side of said fluidized bedcomprises a sidewall and a dome and;

b. said exhaust system comprises an exhaust pipe disposed partiallywithin the combustion chamber on the exhaust side of the fluidized bed,said part of said exhaust pipe disposed within the combustion chamberhaving an opening which is outwardly flared, said opening being remotefrom said dome and said sidewall to prevent the high velocityimpingement of said sticky ashes, salts and molten metals entrained inthe exhaust gas at an angle of incidence near the perpendicular onto thesurface of said flared opening. 3. In a combustor as recited in claim 2wherein said exhaust system further comprises:

a. a second chamber having part of said exhaust pipe 5 disposed therein,said part of said exhaust pipe disposed within said second chamber beingcurved in a radius to form a low velocity centrifugal separator, saidlow velocity centrifugal separator having a discharge port disposedwithin said second charm 1 her.

4. In a combustor as recited in claim 3 wherein: a. said chambercomprises a top, bottom and sidewall; and b. a first ball valvemechanism disposed in the bottom l of said second chamber which opensperiodically to empty ash collected in the bottom of said secondchamber.

5. In a combustor as recited in claim 4 wherein said exhaust systemfurther comprises:

a. a removal conduit partially disposed in the bottom of said secondchamber for removing accumulated solids therefrom, said removal conduithaving an intake port disposed within said second chamber and an exhaustport coupled to said first ball valve mechanism;

b. an intermediate airlock having an intake port and an exhaust port,said intake port of said airlock being coupled to said first ball valve;

c. a second ball valve mechanism, said second ball valve mechanism beingcoupled to said exhaust port of said airlock;

d. a cooling means coupled to said removal conduit and to saidintermediate airlock to cool solids contained therein; and

e. an exhaust pipe disposed within the sidewall of said chamber, saidexhaust pipe having an outwardly flared opening located within saidchamber remote from said top, bottom and sidewall and a discharge portlocated outside said chamber.

6. In a combustor as recited in claim 5 wherein said exhaust systemfurther comprises;

a. a collecting cone disposed within the bottom of said chamber, saidcone having an apical section coupled to said intake port of saidremoval conduit; and

b. a conical wire mesh screen disposed in the bottom of said chamber,said wire mesh screen having a base coupled to said collecting cone andan apical section extending upward into said chamber.

1. In a fluidized bed combustor which burns waste materials of the typethat produce sticky ashes, salts and molten metals which form slag thatadheres to the interior surfaces of the combustor, the combinationcomprising: a. a fluidized bed disposed within a combustion chamberhaving intake and exhaust sides; b. a pressurized air supply coupled tothe intake side of said fluidized bed; c. a pressurized source of wastematerial coupled to the intake side of said fluidized bed; d. meanscoupled to said exhaust side of said fluidized bed for removing saidsticky ashes, salts and molten metals and exhaust gases from saidcombustion chamber while they are at or above the temperature at whichthe sticky ashes, salts and molten metals begin to adhere to saidinterior surfaces of the combustor, said means comprising an exhaustsystem which maintains the velocity of said sticky ashes, salts andmolten metals entrained within said exhaust gas below a velocity whichproduces their agglomeration on interior surfaces of said combustionchamber and said exhaust system.
 2. In a combustor as recited in claim 1wherein: a. said combustion chamber on the exhaust side of saidfluidized bed comprises a sidewall and a dome and; b. said exhaustsystem comprises an exhaust pipe disposed partially within thecombustion chamber on the exhaust side of the fluidized bed, said partof said exhaust pipe disposed within the combustion chamber having anopening which is outwardly flared, said opening being remote from saiddome and said sidewall to prevent the high velocity impingement of saidsticky ashes, salts and molten metals entrained in the exhaust gas at anangle of incidence near the perpendicular onto the surface of saidflared opening.
 3. In a combustor as recited in claim 2 wherein saidexhaust system further comprises: a. a second chamber having part ofsaid exhaust pipe disposed therein, said part of said exhaust pipedisposed within said second chamber being curved in a radius to form alow velocity centrifugal separator, said low velocity centrifugalseparator having a discharge port disposed within said second chamber.4. In a combustor as recited in claim 3 wherein: a. said chambercomprises a top, bottom and sidewall; and b. a first ball valvemechanism disposed in the bottom of said second chamber which opensperiodically to empty ash collected in the bottom of said secondchamber.
 5. In a combustor as recited in claim 4 wherein said exhaustsystem further comprises: a. a removal conduit partially disposed in thebottom of said second chamber for removing accumulated solids therefrom,said removal conduit having an intake port disposed within said secondchamber and an exhaust port coupled to said first ball valve mechanism;b. an intermediate airlock having an intake port and an exhaust port,said intake port of said airlock being coupled to said first ball valve;c. a second ball valve mechanism, said second ball valve mechanism beingcoupled to said exhaust port of said airlock; d. a cooling means coupledto said removal conduit and to said intermediate airlock to cool solidscontained therein; and e. an exhaust pipe disposed within the sidewallof said chamber, said exhaust pipe having an outwardly flared openinglocated within said chamber remote from said top, bottom and sidewalland a discharge port located outside said chamber.
 6. In a combustor asrecited in claim 5 wherein said exhaust system further comprises; a. acollecting cone disposed within the bottom of said chamber, said conehaving an apical section coupled to said intake port of said removalconduit; and b. a conical wire mesh screen disposed in the bottom ofsaid chamber, said wire mesh screen having a base coupled to saidcollecting cone and an apical section extending upward into saidchamber.